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<p>The <a href="index.html">Trusty</a> API generally describes the
Trusty inter-process communication (IPC)
system, including communications with the non-secure world. This page defines the
relevant terms and provides a reference for the API
calls.</p>

<h2 id=ports_and_channels>Ports and channels</h2>

<p>Ports are used by Trusty applications to expose service end-points in the form
of a named path to which clients connect. This gives a simple, string-based
service ID for clients to use. The naming convention is reverse-DNS-style
naming, e.g. <code>com.google.servicename</code>.</p>

<p>When a client connects to a port, the client receives a channel for interacting
with a service. The service must accept an incoming connection, and when it
does, it too receives a channel. In essence, ports are used to look up services
and then communication occurs over a pair of connected channels (i.e.,
connection instances on a port). When a client connects to a port, a symmetric,
bi-directional connection is established. Using this full-duplex path, clients
and servers can exchange arbitrary messages until either side decides to tear
down the connection.</p>

<p>Only secure-side trusted applications or Trusty kernel modules can create
ports. Applications running on the non-secure side (in the normal world) can
only connect to services published by the secure side.</p>

<p>Depending on requirements, a trusted application can be both a client and a
server at the same time. A trusted application that publishes a service (as a
server) might need to connect to other services (as a client).</p>

<h2 id=handle_api>Handle API</h2>

<p>Handles are unsigned integers representing resources such as ports and
channels, similar to file descriptors in UNIX. After handles are created, they
are placed into an application-specific handle table and can be referenced
later.</p>

<p>A caller can associate private data with a handle by using
the <code>set_cookie()</code> method.</p>

<h3 id=methods_handle_api>Methods in the Handle API</h3>

<p>Handles are only valid in the context of an application. An application should
not pass the value of a handle to other applications unless explicitly
specified. A handle value only should be interpreted by comparing it with
the <code>INVALID_IPC_HANDLE #define,</code> which an application can use as an
indication that a handle is invalid or unset.</p>

<h4 id=set_cookie>set_cookie()</h4>

<p>Associates the caller-provided private data with a specified handle.</p>

<pre class="prettyprint">
long set_cookie(uint32_t handle, void *cookie)
</pre>

<p>[in] <code>handle</code>: Any handle returned by one of the API calls</p>

<p>[in] <code>cookie</code>: Pointer to arbitrary user-space data in the Trusty application</p>

<p>[retval]: <code>NO_ERROR</code> on success, <code>&lt; 0</code> error code otherwise</p>

<p>This call is useful for handling events when they occur at a later time after
the handle has been created. The event-handling mechanism supplies the handle
and its cookie back to the event handler.</p>

<p>Handles can be waited upon for events by using the <code>wait()</code>
or <code>wait_any()</code> calls.</p>

<h4 id=wait>wait()</h4>

<p>Waits for an event to occur on a given handle for specified period of time.</p>

<pre class="prettyprint">
long wait(uint32_t handle_id, uevent_t *event, unsigned long timeout_msecs)
</pre>

<p>[in] <code>handle_id</code>: Any handle returned by one of the API calls</p>

<p>[out] <code>event</code>: A pointer to the structure representing
an event that occurred on this handle</p>

<p>[in] <code>timeout_msecs</code>: A timeout value in milliseconds; a
value of -1 is an infinite timeout</p>

<p>[retval]: <code>NO_ERROR</code> if a valid event occurred within a
specified timeout interval; <code>ERR_TIMED_OUT</code> if a specified timeout elapsed but no
event has occurred; <code>&lt; 0</code> for other errors</p>

<h4 id=wait_any>wait_any()</h4>

<p>Waits for any event to occur on any handle in the application handle table for
the specified period of time.</p>

<pre class="prettyprint">
long wait_any(uevent_t *event, unsigned long timeout_msecs);
</pre>

<p>[out] <code>event</code>: A pointer to the structure representing an
event that occurred on this handle</p>

<p>[in] <code>timeout_msecs</code>: A timeout value in milliseconds.
A value of -1 is an infinite timeout</p>

<p>[retval]: <code>NO_ERROR</code> if a valid event occurred within a
specified timeout interval; <code>ERR_TIMED_OUT</code> if a specified timeout elapsed but no
event has occurred; <code>&lt; 0</code> for other errors</p>

<p>Upon success (<code>retval == NO_ERROR</code>), the <code>wait()</code>
and <code>wait_any()</code> calls
fill a specified <code>uevent_t</code> structure with information about
the event that occurred.</p>

<pre class="prettyprint">
typedef struct uevent {
    uint32_t handle; /* handle this event is related to */
    uint32_t event;  /* combination of IPC_HANDLE_POLL_XXX flags */
    void    *cookie; /* cookie associated with this handle */
} uevent_t;
</pre>

<p>The <code>event</code> field contains a combination of the following values:</p>

<pre class="prettyprint">
enum {
  IPC_HANDLE_POLL_NONE    = 0x0,
  IPC_HANDLE_POLL_READY   = 0x1,
  IPC_HANDLE_POLL_ERROR   = 0x2,
  IPC_HANDLE_POLL_HUP     = 0x4,
  IPC_HANDLE_POLL_MSG     = 0x8,
  IPC_HANDLE_POLL_SEND_UNBLOCKED = 0x10,
   more values[TBD]
};
</pre>

<p><code>IPC_HANDLE_POLL_NONE</code> - no events are actually pending,
caller should restart the wait</p>

<p><code>IPC_HANDLE_POLL_ERROR</code> - an unspecified internal error has occurred</p>

<p><code>IPC_HANDLE_POLL_READY</code> - depends on the handle type, as follows:</p>

<ul>
  <li>For ports, this value indicates that there is a pending connection
  <li>For channels, this value indicates that an asynchronous connection
  (see <code>connect()</code>) was established
</ul>

<p>The following events are only relevant for channels:</p>

<ul>
  <li><code>IPC_HANDLE_POLL_HUP</code> - indicates that a channel has been closed by a peer
  <li><code>IPC_HANDLE_POLL_MSG</code> - indicates that there is a pending message for this channel
  <li><code>IPC_HANDLE_POLL_SEND_UNBLOCKED</code> - indicates that a previously
  send-blocked caller may attempt to send a
  message again (see the description of <code>send_msg()</code> for details)
</ul>

<p>An event handler should be prepared to handle a combination of specified
events, as multiple bits might be set at the same time. For example, for a
channel, it is possible to have pending messages, and a connection closed by a
peer at the same time.</p>

<p>Most events are sticky. They persist as long as the underlying condition
persists (for example all pending messages are received and pending connection
requests are handled). The exception is the case of
the <code>IPC_HANDLE_POLL_SEND_UNBLOCKED</code> event, which
is cleared upon a read and the application has only one chance to
handle it.</p>

<p>Handles can be destroyed by calling the <code>close()</code> method.</p>

<h4 id=close>close()</h4>

<p>Destroys the resource associated with the specified handle and removes it from
the handle table.</p>

<pre class="prettyprint">
long close(uint32_t handle_id);
</pre>

<p>[in] <code>handle_id</code>: Handle to destroy</p>

<p>[retval]: 0 if success; a negative error otherwise</p>

<h2 id=server_api>Server API</h2>

<p>A server begins by creating one or more <strong>named ports</strong> representing
its service end-points. Each port is represented by a handle.</p>

<h3 id=methods_server_api>Methods in the Server API</h3>

<h4 id=port_create>port_create()</h4>

<p>Creates a named service port.</p>

<pre class="prettyprint">
long port_create (const char *path, uint num_recv_bufs, size_t recv_buf_size,
uint32_t flags)
</pre>

<p>[in] <code>path</code>: The string name of the port (as described above). This
name should be unique across the system; attempts to create a duplicate will fail.</p>

<p>[in] <code>num_recv_bufs</code>: The maximum number of buffers that a channel on
this port can pre-allocate to facilitate the exchange of data with the client. Buffers are counted
separately for data going in both directions, so specifying 1 here would mean 1
send and 1 receive buffer are preallocated. In general, the number of buffers
required depends on the higher-level protocol agreement between the client and
server. The number can be as little as 1 in case of a very synchronous protocol
(send message, receive reply before sending another). But the number can be
more if the client expects to send more than one message before a reply can
appear (e.g, one message as a prologue and another as the actual command). The
allocated buffer sets are per channel, so two separate connections (channels)
would have separate buffer sets.</p>

<p>[in] <code>recv_buf_size</code>: Maximum size of each individual buffer in the
above buffer set. This value is
protocol-dependent and effectively limits maximum message size you can exchange
with peer</p>

<p>[in] <code>flags</code>: A combination of flags that specifies additional port behavior</p>

<p>This value should be a combination of the following values:</p>

<p><code>IPC_PORT_ALLOW_TA_CONNECT</code> - allows a connection from other secure apps</p>

<p><code>IPC_PORT_ALLOW_NS_CONNECT</code> - allows a connection from the non-secure world</p>

<p>[retval]: Handle to the port created if non-negative or a specific error if
negative</p>

<p>The server then polls the list of port handles for incoming connections
using <code>wait()</code> or <code>wait_any()</code> calls. Upon receiving a connection
request indicated by the <code>IPC_HANDLE_POLL_READY</code> bit set in
the <code>event</code> field of the <code>uevent_t</code> structure, the
server should call <code>accept()</code> to finish establishing a connection and create a
channel (represented by
another handle) that can then be polled for incoming messages.</p>

<h4 id=accept>accept()</h4>

<p>Accepts an incoming connection and gets a handle to a channel.</p>

<pre class="prettyprint">
long accept(uint32_t handle_id, uuid_t *peer_uuid);
</pre>

<p>[in] <code>handle_id</code>: Handle representing the port to which a client has connected</p>

<p>[out] <code>peer_uuid</code>: Pointer to a <code>uuud_t</code> structure to be
filled with the UUID of the connecting client application. It
will be set to all zeros if the connection originated from the non-secure world</p>

<p>[retval]: Handle to a channel (if non-negative) on which the server can
exchange messages with the client (or an error code otherwise)</p>

<h2 id=client_api>Client API</h2>

<p>This section contains the methods in the Client API.</p>

<h3 id=methods_client_api>Methods in the Client API</h3>

<h4 id=connect>connect()</h4>

<p>Initiates a connection to a port specified by name.</p>

<pre class="prettyprint">
long connect(const char *path, uint flags);
</pre>

<p>[in] <code>path</code>: Name of a port published by a Trusty application</p>

<p>[in] <code>flags</code>: Specifies additional, optional behavior</p>

<p>[retval]: Handle to a channel over which messages can be exchanged with the
server; error if negative</p>

<p>If no <code>flags</code> are specified (the <code>flags</code> parameter
is set to 0), calling <code>connect()</code> initiates a synchronous connection
to a specified port that immediately
returns an error if the port does not exist, and creates a block until the
server otherwise accepts a connection.</p>

<p>This behavior can be altered by specifying a combination of two values,
described below:</p>

<pre class="prettyprint">
enum {
IPC_CONNECT_WAIT_FOR_PORT = 0x1,
IPC_CONNECT_ASYNC = 0x2,
};
</pre>

<p><code>IPC_CONNECT_WAIT_FOR_PORT</code> - forces a <code>connect()</code>
call to wait if the specified port does not immediately exist at execution,
instead of failing immediately.</p>

<p><code>IPC_CONNECT_ASYNC</code> - if set, initiates an asynchronous connection. An
application has to poll for
the returned handle (by calling <code>wait()</code> or <code>wait_any()</code>) for
a connection completion event indicated by the <code>IPC_HANDLE_POLL_READY</code>
bit set in the event field of the <code>uevent_t</code> structure before starting
normal operation.</p>

<h2 id=messaging_api>Messaging API</h2>

<p>The Messaging API calls enable the sending and reading of messages over a
previously established connection (channel). The Messaging API calls are the
same for servers and clients.</p>

<p>A client receives a handle to a channel by issuing a <code>connect()</code>
call, and a server gets a channel handle from an <code>accept()</code> call,
described above.</p>

<h4 id=structure_of_a_trusty_message>Structure of a Trusty message</h4>

<p>As shown in the following, messages exchanged by the Trusty API have a minimal
structure, leaving it to the server and client to agree on the semantics of the
actual contents:</p>

<pre class="prettyprint">
/*
 *  IPC message
 */
typedef struct iovec {
        void   *base;
        size_t  len;
} iovec_t;

typedef struct ipc_msg {
        uint     num_iov; /* number of iovs in this message */
        iovec_t  *iov;    /* pointer to iov array */

        uint     num_handles; /* reserved, currently not supported */
        handle_t *handles;    /* reserved, currently not supported */
} ipc_msg_t;
</pre>

<p>A message can be composed of one or more non-contiguous buffers represented by
an array of <code>iovec_t</code> structures. Trusty performs scatter-gather
reads and writes to these blocks
using the <code>iov</code> array. The content of buffers that can be described
by the <code>iov</code> array is completely arbitrary.</p>

<h3 id=methods_messaging_api>Methods in the Messaging API</h3>

<h4 id=send_msg>send_msg()</h4>

<p>Sends a message over a specified channel.</p>

<pre class="prettyprint">
long send_msg(uint32_t handle, ipc_msg_t *msg);
</pre>

<p>[in] <code>handle</code>: Handle to the channel over which to send the message</p>

<p>[in] <code>msg</code>: Pointer to the <code>ipc_msg_t structure</code> describing the message</p>

<p>[retval]: Total number of bytes sent on success; a negative error otherwise</p>

<p>If the client (or server) is trying to send a message over the channel and
there is no space in the destination peer message queue, the channel might
enter a send-blocked state (this should never happen for a simple synchronous
request/reply protocol but might happen in more complicated cases) that is
indicated by returning an <code>ERR_NOT_ENOUGH_BUFFER</code> error code.
In such a case the caller must wait until the peer frees some
space in its receive queue by retrieving the handling and retiring messages,
indicated by the <code>IPC_HANDLE_POLL_SEND_UNBLOCKED</code> bit set in
the <code>event</code> field of the <code>uevent_t</code> structure
returned by the <code>wait()</code> or <code>wait_any()</code> call.</p>

<h4 id=get_msg>get_msg()</h4>

<p>Gets meta-information about the next message in an incoming message queue</p>

<p>of a specified channel.</p>

<pre class="prettyprint">
long get_msg(uint32_t handle, ipc_msg_info_t *msg_info);
</pre>

<p>[in] <code>handle</code>: Handle of the channel on which a new message must be retrieved</p>

<p>[out] <code>msg_info</code>: Message information structure described as follows:</p>

<pre class="prettyprint">
typedef struct ipc_msg_info {
        size_t    len;  /* total message length */
        uint32_t  id;   /* message id */
} ipc_msg_info_t;
</pre>

<p>Each message is assigned a unique ID across the set of outstanding messages,
and the total length of each message is filled in. If configured and allowed by the
protocol, there can be multiple outstanding (opened) messages at once for a
particular channel.</p>

<p>[retval]: <code>NO_ERROR</code> on success; a negative error otherwise</p>

<h4 id=read_msg>read_msg()</h4>

<p>Reads the content of the message with the specified ID starting from the
specified offset.</p>

<pre class="prettyprint">
long read_msg(uint32_t handle, uint32_t msg_id, uint32_t offset, ipc_msg_t
*msg);
</pre>

<p>[in] <code>handle</code>: Handle of the channel from which to read the message</p>

<p>[in] <code>msg_id</code>: ID of the message to read</p>

<p>[in] <code>offset</code>: Offset into the message from which to start reading</p>

<p>[in] <code>msg</code>: Pointer to the <code>ipc_msg_t</code> structure describing
a set of buffers into which to store incoming message
data</p>

<p>[retval]: Total number of bytes stored in the <code>dst</code> buffers on
success; a negative error otherwise</p>

<p>The <code>read_msg</code> method can be called multiple times starting at
a different (not necessarily
sequential) offset as needed.</p>

<h4 id=put_msg>put_msg()</h4>

<p>Retires a message with a specified ID.</p>

<pre class="prettyprint">
long put_msg(uint32_t handle, uint32_t msg_id);
</pre>

<p>[in] <code>handle</code>: Handle of the channel on which the message has arrived</p>

<p>[in] <code>msg_id</code>: ID of message being retired</p>

<p>[retval]: <code>NO_ERROR</code> on success; a negative error otherwise</p>

<p>Message content cannot be accessed after a message has been retired and the
buffer it occupied has been freed.</p>

<h2 id=file_descriptor_api>File Descriptor API</h2>

<p>The File Descriptor API includes <code>read()</code>, <code>write()</code>,
and <code>ioctl()</code> calls. All of these calls can operate on a predefined (static) set of file
descriptors traditionally represented by small numbers. In the current
implementation, the file descriptor space is separate from the IPC handle
space. The File Descriptor API in Trusty is
similar to a traditional file descriptor-based API.</p>

<p>By default, there are 3 predefined (standard and well-known) file descriptors:</p>

<ul>
  <li>0 - standard input. The default implementation of standard input <code>fd</code>
  is a no-op (as trusted applications are not expected to have an interactive
console) so reading, writing or invoking <code>ioctl()</code> on <code>fd</code> 0
should return an <code>ERR_NOT_SUPPORTED</code> error.
  <li>1 - standard output. Data written to standard output can be routed (depending
on the LK debug level) to UART and/or a memory log available on the non-secure
side, depending on the platform and configuration. Non-critical debug logs and
messages should go in standard output. The <code>read()</code> and <code>ioctl()</code>
methods are no-ops and should return an <code>ERR_NOT_SUPPORTED</code> error.
  <li>2 - standard error. Data written to standard error should be routed to the UART
or memory log available on the non-secure side, depending on the platform and
configuration. It is recommended to write only critical messages to standard
error, as this stream is very likely to be unthrottled. The <code>read()</code> and
<code>ioctl()</code> methods are no-ops and should return an <code>ERR_NOT_SUPPORTED</code> error.
</ul>

<p>Even though this set of file descriptors can be extended to implement more
<code>fds</code> (to implement platform-specific extensions), extending file descriptors needs
to be exercised with caution. Extending file descriptors is prone to create
conflicts and is not generally recommended.</p>

<h3 id=methods_file_descriptor_api>Methods in the File Descriptor API</h3>

<h4 id=read>read()</h4>

<p>Attempts to read up to <code>count</code> bytes of data from a specified file descriptor.</p>

<pre class="prettyprint">
long read(uint32_t fd, void *buf, uint32_t count);
</pre>

<p>[in] <code>fd</code>: File descriptor from which to read</p>

<p>[out] <code>buf</code>: Pointer to a buffer into which to store data</p>

<p>[in] <code>count</code>: Maximum number of bytes to read</p>

<p>[retval]: Returned number of bytes read; a negative error otherwise</p>

<h4 id=write>write()</h4>

<p>Writes up to <code>count</code> bytes of data to specified file descriptor.</p>

<pre class="prettyprint">
long write(uint32_t fd, void *buf, uint32_t count);
</pre>

<p>[in] <code>fd</code>: File descriptor to which to write</p>

<p>[out] <code>buf</code>: Pointer to data to write</p>

<p>[in] <code>count</code>: Maximum number of bytes to write</p>

<p>[retval]: Returned number of bytes written; a negative error otherwise</p>

<h4 id=ioctl>ioctl()</h4>

<p>Invokes a specified <code>ioctl</code> command for a given file descriptor.</p>

<pre class="prettyprint">
long ioctl(uint32_t fd, uint32_t cmd, void *args);
</pre>

<p>[in] <code>fd</code>: File descriptor on which to invoke <code>ioctl()</code></p>

<p>[in] <code>cmd</code>: The <code>ioctl</code> command</p>

<p>[in/out] <code>args</code>: Pointer to <code>ioctl()</code> arguments</p>

<h2 id=miscellaneous_api>Miscellaneous API</h2>

<h3 id=methods_misc_api>Methods in the Miscellaneous API</h3>

<h4 id=gettime>gettime()</h4>

<p>Returns the current system time (in nanoseconds).</p>

<pre class="prettyprint">
long gettime(uint32_t clock_id, uint32_t flags, uint64_t *time);
</pre>

<p>[in] <code>clock_id</code>: Platform-dependent; pass zero for default</p>

<p>[in] <code>flags</code>: Reserved, should be zero</p>

<p>[in] <code>time</code>: Pointer to an <code>int64_t</code> value to which to store the current time</p>

<p>[retval]: <code>NO_ERROR</code> on success; a negative error otherwise</p>

<h4 id=nanosleep>nanosleep()</h4>

<p>Suspends execution of the calling application for a specified period of time
and resumes it after that period.</p>

<pre class="prettyprint">
long nanosleep(uint32_t clock_id, uint32_t flags, uint64_t sleep_time)
</pre>

<p>[in] <code>clock_id</code>: Reserved, should be zero</p>

<p>[in] <code>flags</code>: Reserved, should be zero</p>

<p>[in] <code>sleep_time</code>: Sleep time in nanoseconds</p>

<p>[retval]: <code>NO_ERROR</code> on success; a negative error otherwise</p>

<h2 id=example_of_a_trusted_application_server>Example of a trusted application server</h2>

<p>The following sample application shows the usage of the above APIs. The sample
creates an "echo" service that handles multiple incoming connections and
reflects back to the caller all messages it receives from clients originated
from the secure or non-secure side.</p>

<pre class="prettyprint">
#include &lt;assert.h>
#include &lt;err.h>
#include &lt;stddef.h>
#include &lt;stdio.h>
#include &lt;stdlib.h>
#include &lt;string.h>
#include &lt;trusty_std.h>

#include &lt;app/echo/uuids.h>

#define LOG_TAG "echo_srv"

#define TLOGE(fmt, ...) \
    fprintf(stderr, "%s: %d: " fmt, LOG_TAG, __LINE__,  ## __VA_ARGS__)

#define MAX_ECHO_MSG_SIZE  64

static const char *srv_name = "com.android.echo.srv.echo";

static uint8_t msg_buf[MAX_ECHO_MSG_SIZE];

/*
 *  Message handler
 */
static int handle_msg(handle_t chan)
{
  int rc;
  iovec_t iov;
  ipc_msg_t msg;
  ipc_msg_info_t msg_inf;

  iov.base = msg_buf;
  iov.len  = sizeof(msg_buf);

  msg.num_iov = 1;
  msg.iov = &iov;
  msg.num_handles = 0;
  msg.handles  = NULL;

  /* get message info */
  rc = get_msg(chan, &msg_inf);
  if (rc == ERR_NO_MSG)
    return NO_ERROR; /* no new messages */

  if (rc != NO_ERROR) {
    TLOGE("failed (%d) to get_msg for chan (%d)\n",
          rc, chan);
    return rc;
  }

  /* read msg content */
  rc = read_msg(chan, msg_inf.id, 0, &msg);
  if (rc &lt; 0) {
    TLOGE("failed (%d) to read_msg for chan (%d)\n",
          rc, chan);
    return rc;
  }

  /* update number of bytes received */
  iov.len = (size_t) rc;

  /* send message back to the caller */
  rc = send_msg(chan, &msg);
  if (rc &lt; 0) {
    TLOGE("failed (%d) to send_msg for chan (%d)\n",
          rc, chan);
    return rc;
  }

  /* retire message */
  rc = put_msg(chan, msg_inf.id);
  if ( rc != NO_ERROR) {
    TLOGE("failed (%d) to put_msg for chan (%d)\n",
          rc, chan);
    return rc;
  }

  return NO_ERROR;
}

/*
 *  Channel event handler
 */
static void handle_channel_event(const uevent_t *ev)
{
  int rc;

  if (ev->event & IPC_HANDLE_POLL_MSG) {
    rc = handle_msg(ev->handle);
    if (rc != NO_ERROR) {
      /* report an error and close channel */
      TLOGE("failed (%d) to handle event on channel %d\n",
             rc, ev->handle);
      close(ev->handle);
    }
    return;
  }
  if (ev->event & IPC_HANDLE_POLL_HUP) {
    /* closed by peer. */
    close(ev->handle);
    return;
  }
}

/*
 *  Port event handler
 */
static void handle_port_event(const uevent_t *ev)
{
  uuid_t peer_uuid;

  if ((ev->event & IPC_HANDLE_POLL_ERROR) ||
      (ev->event & IPC_HANDLE_POLL_HUP) ||
      (ev->event & IPC_HANDLE_POLL_MSG) ||
      (ev->event & IPC_HANDLE_POLL_SEND_UNBLOCKED)) {
    /* should never happen with port handles */
    TLOGE("error event (0x%x) for port (%d)\n",
           ev->event, ev->handle);
    abort();
  }
  if (ev->event & IPC_HANDLE_POLL_READY) {
    /* incoming connection: accept it */
    int rc = accept(ev->handle, &peer_uuid);
    if (rc &lt; 0) {
      TLOGE("failed (%d) to accept on port %d\n",
             rc, ev->handle);
      return;
    }
  }
}

/*
 *  Main application entry point
 */
int main(void)
{
  int rc;
  handle_t port;

  /* Initialize service */
  rc = port_create(srv_name, 1, MAX_ECHO_MSG_SIZE,
       IPC_PORT_ALLOW_NS_CONNECT |
       IPC_PORT_ALLOW_TA_CONNECT );
  if (rc &lt; 0) {
    TLOGE("Failed (%d) to create port %s\n",
          rc, srv_name);
    abort();
  }
  port = (handle_t)rc;

  /* enter main event loop */
  while (true) {
    uevent_t ev;

    ev.handle = INVALID_IPC_HANDLE;
    ev.event  = 0;
    ev.cookie = NULL;

    /* wait forever */
    rc = wait_any(&ev, -1);
    if (rc == NO_ERROR) {
      /* got an event */
      if (ev.handle == port) {
        handle_port_event(&ev);
      } else {
        handle_channel_event(&ev);
      }
    } else {
      TLOGE("wait_any returned (%d)\n", rc);
      abort();
    }
  }
  return 0;
}
</pre>

<h2 id=example_of_a_trusted_application_client>Example of a trusted application client</h2>

<p>The following code snippets show the use of the Trusty messaging APIs to
implement a client of an "echo" service (shown in the code above). The <code>sync_connect()</code>
method shows an implementation of a synchronous connect with a timeout on top
of an asynchronous <code>connect()</code> call.</p>

<pre class="prettyprint">
/*
 *  Local wrapper on top of an async connect that provides a
 *  synchronous connect with timeout.
 */
int sync_connect(const char *path, uint timeout)
{
  int rc;
  uevent_t evt;
  handle_t chan;

  rc = connect(path, IPC_CONNECT_ASYNC | IPC_CONNECT_WAIT_FOR_PORT);
  if (rc >= 0) {
    chan = (handle_t) rc;
    rc = wait(chan, &evt, timeout);
    if (rc == 0) {
      rc = ERR_BAD_STATE;
      if (evt.handle == chan) {
        if (evt.event & IPC_HANDLE_POLL_READY)
          return chan;
        if (evt.event & IPC_HANDLE_POLL_HUP)
          rc = ERR_CHANNEL_CLOSED;
      }
    }
    close(chan);
  }
  return rc;
}
</pre>

<p>The <code>run_end_to_end_msg_test()</code> method sends 10,000 messages asynchronously
to the "echo" service and handles
replies.</p>

<pre class="prettyprint">
static int run_echo_test(void)
{
  int rc;
  handle_t chan;
  uevent_t uevt;
  uint8_t tx_buf[64];
  uint8_t rx_buf[64];
  ipc_msg_info_t inf;
  ipc_msg_t   tx_msg;
  iovec_t     tx_iov;
  ipc_msg_t   rx_msg;
  iovec_t     rx_iov;

  /* prepare tx message buffer */
  tx_iov.base = tx_buf;
  tx_iov.len  = sizeof(tx_buf);
  tx_msg.num_iov = 1;
  tx_msg.iov     = &tx_iov;
  tx_msg.num_handles = 0;
  tx_msg.handles = NULL;

  memset (tx_buf, 0x55, sizeof(tx_buf));

  /* prepare rx message buffer */
  rx_iov.base = rx_buf;
  rx_iov.len  = sizeof(rx_buf);
  rx_msg.num_iov = 1;
  rx_msg.iov     = &rx_iov;
  rx_msg.num_handles = 0;
  rx_msg.handles = NULL;

  /* open connection to echo service */
  rc = sync_connect(srv_name, 1000);
  if(rc &lt; 0)
    return rc;

  /* got channel */
  chan = (handle_t)rc;

  /* send/receive 10000 messages asynchronously. */
  uint tx_cnt = 10000;
  uint rx_cnt = 10000;

  while (tx_cnt || rx_cnt) {
    /* send messages until all buffers are full */
while (tx_cnt) {
    rc = send_msg(chan, &tx_msg);
      if (rc == ERR_NOT_ENOUGH_BUFFER)
      break;  /* no more space */
    if (rc != 64) {
      if (rc > 0) {
        /* incomplete send */
        rc = ERR_NOT_VALID;
}
      goto abort_test;
}
    tx_cnt--;
  }

  /* wait for reply msg or room */
  rc = wait(chan, &uevt, 1000);
  if (rc != NO_ERROR)
    goto abort_test;

  /* drain all messages */
  while (rx_cnt) {
    /* get a reply */
      rc = get_msg(chan, &inf);
    if (rc == ERR_NO_MSG)
        break;  /* no more messages  */
  if (rc != NO_ERROR)
goto abort_test;

  /* read reply data */
    rc = read_msg(chan, inf.id, 0, &rx_msg);
  if (rc != 64) {
    /* unexpected reply length */
    rc = ERR_NOT_VALID;
    goto abort_test;
}

  /* discard reply */
  rc = put_msg(chan, inf.id);
  if (rc != NO_ERROR)
    goto abort_test;
  rx_cnt--;
  }
}

abort_test:
  close(chan);
  return rc;
}
</pre>

<h2 id=non-secure_world_apis_and_applications>Non-secure world APIs and applications</h2>

<p>A set of Trusty services, published from the secure side and marked with
the <code>IPC_PORT_ALLOW_NS_CONNECT</code> attribute, are accessible to kernel
and user space programs running on the
non-secure side.</p>

<p>The execution environment on the non-secure side (kernel and user space) is
drastically different from the execution environment on the secure-side.
Therefore, rather than a single library for both environments, there are two
different sets of APIs. In the kernel, the Client API is provided by the
trusty-ipc kernel driver and registers a character device node that can be used
by user space processes to communicate with services running on the secure
side.</p>

<h3 id=user_space_trusty_ipc_client_api>User space Trusty IPC Client API</h3>

<p>The user space Trusty IPC Client API library is a thin layer on top of the
device node <code>fd</code>.</p>

<p>A user space program starts a communication session
by calling <code>tipc_connect()</code>,
initializing a connection to a specified Trusty service. Internally,
the <code>tipc_connect()</code> call opens a specified device node to
obtain a file descriptor and invokes a <code>TIPC_IOC_CONNECT ioctl()</code>
call with the <code>argp</code> parameter pointing to a string containing a
service name to which to connect.</p>

<pre class="prettyprint">
#define TIPC_IOC_MAGIC  'r'
#define TIPC_IOC_CONNECT  _IOW(TIPC_IOC_MAGIC, 0x80, char *)
</pre>

<p>The resulting file descriptor can only be used to communicate with the service
for which it was created. The file descriptor should be closed by
calling <code>tipc_close()</code> when the connection is not required anymore.</p>

<p>The file descriptor obtained by the <code>tipc_connect()</code> call
behaves as a typical character device node; the file descriptor:</p>

<ul>
  <li>Can be switched to non-blocking mode if needed
  <li>Can be written to using a standard <code>write()</code>
  call to send messages to the other side
  <li>Can be polled (using <code>poll()</code> calls or <code>select()</code> calls)
  for availability of incoming messages as a regular file descriptor
  <li>Can be read to retrieve incoming messages
</ul>

<p>A caller sends a message to the Trusty service by executing a write call for
the specified <code>fd</code>. All data passed to the above <code>write()</code> call
is transformed into a message by the trusty-ipc driver. The message is
delivered to the secure side where the data is handled by the IPC subsystem in
the Trusty kernel and routed to the proper destination and delivered to an app
event loop as an <code>IPC_HANDLE_POLL_MSG</code> event on a particular channel
handle. Depending on the particular,
service-specific protocol, the Trusty service may send one or more reply
messages that are delivered back to the non-secure side and placed in the
appropriate channel file descriptor message queue to be retrieved by the user
space application <code>read()</code> call.</p>

<h4 id=tipc_connect>tipc_connect()</h4>

<p>Opens a specified <code>tipc</code> device node and initiates a
connection to a specified Trusty service.</p>

<pre class="prettyprint">
int tipc_connect(const char *dev_name, const char *srv_name);
</pre>

<p>[in] <code>dev_name</code>: Path to the Trusty IPC device node to open</p>

<p>[in] <code>srv_name</code>: Name of a published Trusty service to which to connect</p>

<p>[retval]: Valid file descriptor on success, -1 otherwise.</p>

<h4 id=tipc_close>tipc_close()</h4>

<p>Closes the connection to the Trusty service specified by a file descriptor.</p>

<pre class="prettyprint">
int tipc_close(int fd);
</pre>

<p>[in] <code>fd</code>: File descriptor previously opened by
a <code>tipc_connect()</code> call</p>

<h2 id=kernel_trusty_ipc_client_api>Kernel Trusty IPC Client API</h2>

<p>The kernel Trusty IPC Client API is available for kernel drivers. The user
space Trusty IPC API is implemented on top of this API.</p>

<p>In general, typical usage of this API consists of a caller creating
a <code>struct tipc_chan</code> object by using the <code>tipc_create_channel()</code>
function and then using the <code>tipc_chan_connect()</code> call to initiate a
connection to the Trusty IPC service running on the secure
side. The connection to the remote side can be terminated by
calling <code>tipc_chan_shutdown()</code> followed by
<code>tipc_chan_destroy()</code> to clean up resources.</p>

<p>Upon receiving a notification (through the <code>handle_event()</code> callback)
that a connection has been successfully established, a caller does
the following:</p>

<ul>
  <li>Obtains a message buffer using the <code>tipc_chan_get_txbuf_timeout()</code> call
  <li>Composes a message, and
  <li>Queues the message using the <code>tipc_chan_queue_msg()</code>
  method for delivery to a Trusty service (on the secure side), to which the
channel is connected
</ul>

<p>After queueing is successful, the caller should forget the message buffer
because the message buffer eventually returns to the free buffer pool after
processing by the remote side (for reuse later, for other messages). The user
only needs to call <code>tipc_chan_put_txbuf()</code> if it fails to
queue such buffer or it is not required anymore.</p>

<p>An API user receives messages from the remote side by handling a
<code>handle_msg()</code> notification callback (which is called in
the context of the trusty-ipc <code>rx</code> workqueue) that
provides a pointer to an <code>rx</code> buffer containing an
incoming message to be handled.</p>

<p>It is expected that the <code>handle_msg()</code> callback
implementation will return a pointer to a valid <code>struct tipc_msg_buf</code>.
It can be the same as the incoming message buffer if it is handled locally
and not required anymore. Alternatively, it can be a new buffer obtained by
a <code>tipc_chan_get_rxbuf()</code> call if the incoming buffer is queued
for further processing. A detached <code>rx</code> buffer must be tracked
and eventually released using a  <code>tipc_chan_put_rxbuf()</code> call when
it is no longer needed.</p>

<h3 id=methods_ktic_api>Methods in the Kernel Trusty IPC Client API</h3>

<h4 id=tipc_create_channel>tipc_create_channel()</h4>

<p>Creates and configures an instance of a Trusty IPC channel for a particular
trusty-ipc device.</p>

<pre class="prettyprint">
struct tipc_chan *tipc_create_channel(struct device *dev,
                          const struct tipc_chan_ops *ops,
                              void *cb_arg);
</pre>

<p>[in] <code>dev</code>: Pointer to the trusty-ipc for which the device
channel is created</p>

<p>[in] <code>ops</code>: Pointer to a <code>struct tipc_chan_ops</code>,
with caller-specific
callbacks filled in</p>

<p>[in] <code>cb_arg</code>: Pointer to data that will be passed
to <code>tipc_chan_ops</code> callbacks</p>

<p>[retval]: Pointer to a newly-created instance of
<code>struct tipc_chan</code> on success,
<code>ERR_PTR(err)</code> otherwise</p>

<p>In general, a caller must provide two callbacks that are asynchronously invoked
when the corresponding activity is occurring.</p>

<p>The <code>void (*handle_event)(void *cb_arg, int event)</code>event is invoked
to notify a caller about a channel state change.</p>

<p>[in] <code>cb_arg</code>: Pointer to data passed to a
<code>tipc_create_channel()</code> call</p>

<p>[in] <code>event</code>: An event that can be one of the following values:</p>

<ul>
  <li><code>TIPC_CHANNEL_CONNECTED</code> - indicates a successful connection
  to the remote side
  <li><code>TIPC_CHANNEL_DISCONNECTED</code> - indicates the remote side denied the
  new connection request or requested
disconnection for the previously connected channel
  <li><code>TIPC_CHANNEL_SHUTDOWN</code> - indicates the remote side is shutting down,
  permanently terminating all connections
</ul>

<p>The <code>struct tipc_msg_buf *(*handle_msg)(void *cb_arg, struct tipc_msg_buf *mb)</code>
callback is invoked to provide notification that a new message has been
received over a specified channel:</p>

<ul>
  <li>[in] <code>cb_arg</code>: Pointer to data passed to the
  <code>tipc_create_channel()</code> call
  <li>[in] <code>mb</code>: Pointer to a <code>struct tipc_msg_buf</code>
  describing an incoming message
  <li>[retval]: The callback implementation is expected to return a pointer to a
  <code>struct tipc_msg_buf</code> that can be the same pointer received
  as an
  <code>mb</code> parameter if the message is handled locally and is not
  required anymore (or it
can be a new buffer obtained by the <code>tipc_chan_get_rxbuf()</code> call)
</ul>

<h4 id=tipc_chan_connect>tipc_chan_connect()</h4>

<p>Initiates a connection to the specified Trusty IPC service.</p>

<pre class="prettyprint">
int tipc_chan_connect(struct tipc_chan *chan, const char *port);
</pre>

<p>[in] <code>chan</code>: Pointer to a channel returned by the
<code>tipc_create_chan()</code> call</p>

<p>[in] <code>port</code>: Pointer to a string containing the
service name to which to connect</p>

<p>[retval]: 0 on success, a negative error otherwise</p>

<p>The caller is notified when a connection is established by receiving a
<code>handle_event</code> callback.</p>

<h4 id=tipc_chan_shutdown>tipc_chan_shutdown()</h4>

<p>Terminates a connection to the Trusty IPC service previously initiated
by a <code>tipc_chan_connect()</code> call.</p>

<pre class="prettyprint">
int tipc_chan_shutdown(struct tipc_chan *chan);
</pre>

<p>[in] <code>chan</code>: Pointer to a channel returned by
a <code>tipc_create_chan()</code> call</p>

<h4 id=tipc_chan_destroy>tipc_chan_destroy()</h4>

<p>Destroys a specified Trusty IPC channel.</p>

<pre class="prettyprint">
void tipc_chan_destroy(struct tipc_chan *chan);
</pre>

<p>[in] <code>chan</code>: Pointer to a channel returned by the
<code>tipc_create_chan()</code> call</p>

<h4 id=tipc_chan_get_txbuf_timeout>tipc_chan_get_txbuf_timeout()</h4>

<p>Obtains a message buffer that can be used to send data over a specified
channel. If the buffer is not immediately available the caller may be blocked
for the specified timeout (in milliseconds).</p>

<pre class="prettyprint">
struct tipc_msg_buf *
tipc_chan_get_txbuf_timeout(struct tipc_chan *chan, long timeout);
</pre>

<p>[in] <code>chan</code>: Pointer to the channel to which to queue a message</p>

<p>[in] <code>chan</code>: Maximum timeout to wait until the
<code>tx</code> buffer becomes available </p>

<p>[retval]: A valid message buffer on success,
<code>ERR_PTR(err)</code> on error</p>

<h4 id=tipc_chan_queue_msg>tipc_chan_queue_msg()</h4>

<p>Queues a message to be sent over the specified
Trusty IPC channels.</p>

<pre class="prettyprint">
int tipc_chan_queue_msg(struct tipc_chan *chan, struct tipc_msg_buf *mb);
</pre>

<p>[in] <code>chan</code>: Pointer to the channel to which to queue the message</p>

<p>[in] <code>mb:</code> Pointer to the message to queue
(obtained by a <code>tipc_chan_get_txbuf_timeout()</code> call)</p>

<p>[retval]: 0 on success, a negative error otherwise</p>

<h4 id=tipc_chan_put_txbuf>tipc_chan_put_txbuf()</h4>

<p>Releases the specified <code>Tx</code> message buffer
previously obtained by a <code>tipc_chan_get_txbuf_timeout()</code> call.</p>

<pre class="prettyprint">
void tipc_chan_put_txbuf(struct tipc_chan *chan,
                         struct tipc_msg_buf *mb);
</pre>

<p>[in] <code>chan</code>: Pointer to the channel to which
this message buffer belongs</p>

<p>[in] <code>mb</code>: Pointer to the message buffer to release</p>

<p>[retval]: None</p>

<h4 id=tipc_chan_get_rxbuf>tipc_chan_get_rxbuf()</h4>

<p>Obtains a new message buffer that can be used to receive messages over the
specified channel.</p>

<pre class="prettyprint">
struct tipc_msg_buf *tipc_chan_get_rxbuf(struct tipc_chan *chan);
</pre>

<p>[in] <code>chan</code>: Pointer to a channel to which this message buffer belongs</p>

<p>[retval]: A valid message buffer on success, <code>ERR_PTR(err)</code> on error</p>

<h4 id=tipc_chan_put_rxbuf>tipc_chan_put_rxbuf()</h4>

<p>Releases a specified message buffer previously obtained by a
<code>tipc_chan_get_rxbuf()</code> call.</p>

<pre class="prettyprint">
void tipc_chan_put_rxbuf(struct tipc_chan *chan,
                         struct tipc_msg_buf *mb);
</pre>

<p>[in] <code>chan</code>: Pointer to a channel to which this message buffer belongs</p>

<p>[in] <code>mb</code>: Pointer to a message buffer to release</p>

<p>[retval]: None</p>

  </body>
</html>